1. Field of the Invention
The present invention relates to resist patterns of fine wiring patterns formed on substrates by using a lift off method or other suitable method, and relates to methods for forming such a novel a wiring pattern.
2. Description of the Related Art
Conventionally, a lift-off method for forming metal wiring on various substrates, such as semiconductor substrates, dielectric substrates, and pyroelectric substrates, has been used. When a wiring pattern is formed on a substrate by a lift off method, to ensure superior resist stripability, the cross-section of the resist pattern must have inversely tapered configurations.
Various methods for forming an inversely tapered cross-sectional shape of the resist pattern have been used. As an example, a method is disclosed in Japanese Unexamined Patent Application Publication No. 2-137224 in which a resist is defined by a plurality of organic layers. In the method described above, as schematically shown in FIG. 1A, a first resist layer 11 having outstanding stripability, a second resist layer 12 having outstanding heat resistance, and a third resist layer 13 composed of a resist having a high resistance to dry etching and having superior heat resistance or composed of an ionizing radiation resist are sequentially formed on and above a semiconductor substrate 10 from the substrate side, in that order. In the three-layer laminated structure described above, after the third resist layer 13 disposed as the topmost layer is first patterned by a photolithographic method or other suitable method (FIG. 2B), dry etching is performed on the resist. As a result, the second and the first resist layers are removed through openings in the third resist layer 13, whereby patterning of the resist is performed. In the step described above, since the third resist layer 13 has higher resistance to dry etching, the etching rate thereof is controlled to be very low, and on the other hand, since the second and the first resist layers are etched at normal etching rates, as a result, a resist pattern having inversely tapered cross-sectional configurations, as shown in FIG. 1C, are produced.
As described above, in the conventional resist patterns, since resist patterns are produced having inversely tapered cross-sectional configurations and also having superior heat resistance, there are advantages in which patterns of metal wiring, an inorganic compound, an organic compound are formed at a higher temperature.
In a lift off method, a photolithographic process is generally used, and problems occur in the exposure in the photolithographic process. In particular, light incident on the resist and reflected light (which is produced when the incident light is reflected by the substrate) interfere with each other, and in some cases standing waves are generated. Due to the presence of standing waves, the side surfaces of openings in the resist have wave shapes. When the resist has wave shapes, desired line widths formed by a lift off method cannot be controlled.
Conventionally, a method for reducing the wave shapes is used to offset the problems caused thereby in which a photosensitive agent is uniformly diffused by a baking treatment (PEB treatment) performed after exposure.
However, recently, concomitant with the formation of finer wiring patterns, the formation of thinner resist films and improvements in transparency thereof are available. When the formation of thinner resist films and the improvement in transparency thereof are used, the amount of light reflected from the substrate is increased, and as a result, it is difficult to reduce the effects of the standing waves merely by the conventional PEB treatment.
To reduce the effects of the standing waves described above, a method in which a transparent substrate is used having a roughened rear surface has been used. However, when this type of transparent substrate is used, even though the effects of the standing waves are reduced, a new problem occurs in which exposure light is diffusely reflected at the rear surface of the substrate, and the resist is re-exposed from the rear surface side of the substrate (when re-exposure occurs by diffuse reflection, variation occurs in the line widths of the resist pattern).
Furthermore, when a pyroelectric substrate is used, the problems described below may also occur. That is, increases and decreases in temperature are repeatedly performed in a sequential process of resist coating, exposure, a PEB treatment, and other process. According to the change in temperature as described above, a high voltage is generated in the pyroelectric substrate, and hence, discharges therefrom occur in many cases. Due to the discharges described above, for example, a resist having electron beam sensitivity partially reacts, and non-reacted portions are present together with unintentionally reacted portions in the resist, a resist having uniform characteristics cannot be obtained.
To overcome the above described problems with the prior art, preferred embodiments of the present invention provide a resist pattern which reduces the effects of standing waves, and is produced by the interference between incident light and reflected light, in a photolithographic process of a lift off method to provide fine wiring patterns, and provide a method for providing wiring using the resist pattern described above. In addition, even where a pyroelectric substrate is used as a substrate, preferred embodiments of the present invention provide a resist pattern having uniform characteristics.
The resist pattern provided on a substrate, includes a substrate, a first resist layer provided on the substrate and defined by a first organic material which dissolves in an organic solvent, water, or a solvent primarily composed of water, a second resist layer defined by a second organic material provided on the first resist layer, the second organic material having a high absorbance of a light of a particular wavelength, and a third resist layer defined by a third organic material provided on the second resist layer, the organic material having a resistance to dry etching and being photosensitive to the light.
The method for providing a wiring pattern, preferably includes the steps of forming a first resist layer on the substrate, the first resist layer being defined by a first organic material which dissolves in an organic solvent, water, or a solvent primarily composed of water, forming a second resist layer on the first resist layer, the second resist layer being defined by a second organic material which has a high absorbance of a light having a particular wavelength, and forming a third resist layer on the second resist layer, the third resist layer being defined by a third organic material provided which has a resistance to dry etching and is photosensitive to the light, exposing the third resist layer using the light through a mask pattern having an opening, developing the third resist layer to provide the opening therein, etching the second and third resist layers via the opening of the first resist layer such that the opening extends to the substrate, thereby forming a resist pattern having the opening, and forming a metal wiring pattern on the substrate through the resist pattern.
The substrate may have a pyroelectric property, and the first organic material preferably has no electron beam sensitivity.
The first, second and third organic materials may have heat resistivity. The first, second and third organic materials preferably do not deform at a temperature of at least approximately 140xc2x0 C. The first organic material preferably includes polydimethyl glutarimide.
The first, second and third resist patterns preferably have an opening that exposes the substrate and has a tapered shape.
As is apparent from the description above, according to the resist pattern and to the method for forming wiring of various preferred embodiments of the present invention, since a material is used for the first resist layer, which easily dissolves in an organic solvent and has superior stripability, and a material is used for the third resist layer, which has high resistance to dry etching, a resist pattern is provided which has inversely tapered cross-sectional shapes and is easily stripped off by a solvent, as is obtained by conventional techniques. Since the resist pattern also has superior heat resistance, patterns of metal wiring, an inorganic compound, and an organic compound are formed at a high temperature. In addition, since the second resist layer is defined by a material having a high level of absorbance of exposure wavelengths, incident light passing through the third resist layer disposed at an upper side is absorbed in the second resist layer, and light does not reflect from the substrate. As a result, the effects of standing waves caused by the interference between the incident light and the reflected light is greatly reduced, unlike in conventional techniques. Hence, a resist pattern suitable for forming very fine wiring is obtained. Furthermore, where a transparent substrate having a roughened rear surface is used, since incident light passing through the third resist layer is absorbed in the second resist layer, diffuse reflection does not occur at the rear surface of the substrate, and hence, variations in the line widths of the patterns are greatly reduced. In addition, when a resist pattern having the structure of various preferred embodiments of the present invention is used, and when a PEB treatment is also performed, the occurrence of wave shapes at side surfaces of the openings in the resist, which are caused by the effects of standing waves, is greatly reduced and minimized.
In addition, when a resist pattern is provided on a pyroelectric substrate, by using a material having high solubility in an organic solvent and having no electron beam sensitivity for the first resist layer described above, a resist pattern having uniform characteristics is provided in which non-reacted portions and reacted portions are not present together in the pattern.
In addition, by using a material for the first resist layer, which has high solubility in water or a solvent primarily composed of water, the quantity of an organic solvent used is greatly reduced, and a production process which is much less detrimental to the environment is achieved.
Furthermore, by providing wiring using the resist pattern of preferred embodiments of the present invention, finer line widths are accurately provided in accordance with the designed fine wiring, compared to that provided by the conventional method, and hence, a method for forming wiring is provided which is suitable to produce miniaturized electronic devices and for greatly improving the high frequency characteristics thereof.
For the purpose of illustrating the invention, there is shown in the drawings several forms which are presently preferred, it being understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown.
Other features, elements, characteristics and advantages of the present invention will become more apparent from the detailed description of preferred embodiments thereof with reference to the drawings.